1. Field of the Invention
This invention relates to a process of preparing an alkenyl-substituted aromatic compound from an aromatic compound and an alkane. More particularly, the present invention relates to a process of producing styrene, where benzene, hydrogen chloride and oxygen are reacted in the presence of a catalyst to yield reaction products comprising chlorinated benzene and water, and wherein the chlorinated benzene is reacted with ethane to produce styrene and hydrogen chloride.
2. Description of the Background
Alkenyl-substituted aromatic compounds, such as styrene and α-methylstyrene, are used in the production of thermoplastic polymers, such as, polystyrenes, acrylonitrile-butadiene-styrene copolymers (ABS), styrene-acrylonitrile resins (SAN), styrene-butadiene elastomeric copolymers (SBR), and formulations for unsaturated polyester resins. Divinylbenzene is also used as a polymerization monomer for special synthetic rubbers.
Styrene is generally prepared by the adiabatic or isothermic catalytic dehydrogenation of ethylbenzene in the presence of catalysts selected from metal oxides or their mixtures. Ethylbenzene is prepared by the alkylation of benzene, available as a refinery product, with ethylene coming from the cracking or dehydrogenation of ethane. Ethylene is typically derived from the thermal or steam cracking of saturated hydrocarbons rich in natural gas, ethane, propane, and butanes, or from the cracking of naptha. The alkylation reaction can be carried out in the vapor phase, using zeolite catalysts with high SiO2/Al2O3 ratios, for example zeolites of the type ZSM-5 or Lewis acids, or in liquid phase. Alternatively, ethylbenzene can be produced from a dilute ethylene stream in a mixed phase reactor, as disclosed by ABB Lummus Global and CDTech in U.S. Pat. No. 5,756,872.
The traditional methods for the production of styrene generally require the availability of ethylene for the preparation of ethylbenzene. The conventional method of preparing styrene possesses disadvantages in several regards. The crackers used to prepare ethylene are highly costly to construct and maintain, and their operation is energy intensive. In addition, the styrene production facility must be located at the site of the cracker, because the transportation of ethylene is too expensive. Finally, the ethylene needed for the alkylation step is required to be essentially pure, otherwise undesirable alkylated products are produced and the lifetime of the alkylation catalyst is significantly reduced. Since ethane cracking produces a variety of products in addition to ethylene including, for example, propylene, acetylene, C4 saturated and unsaturated hydrocarbons, and C5 and C9 or higher hydrocarbons, the effluent from the cracker must be separated, for example, by extractive distillation and/or selective hydrogenation, to obtain pure ethylene. These separations significantly increase the cost of producing ethylene.
The more recent technology of using dilute ethylene streams derived from off-gases from fluid catalytic cracker operations possess similar disadvantages to those mentioned above. The requirement of a suitable ethylene stream accounts for about 40 percent of the raw material cost of ethylbenzene.
An alternative process to cracking generates ethylene from the dehydrogenation of ethane, as disclosed in U.S. Pat. No. 5,430,211 and EP-B1-0,637,578. These processes rely on selective catalysts, such as platinum and/or gallium to produce clean, dilute streams of ethylene in ethane. Dilute ethylene streams produced from these dehydrogenation processes are known to successfully alkylate benzene to ethylbenzene, as disclosed, for example, in U.S. Pat. No. 5, 430,211 of The Dow Chemical Company.